(CNN) -- A 19-year-old mathematics major from Austin, Texas, was identified Tuesday as the suspected gunman who fired shots from an AK-47 and then turned the gun on himself, the University of Texas at Austin said.

The Travis County Medical Examiner identified Colton Tooley, a sophomore at the university, as the campus shooter.

No one else was injured in the incident. Tooley's motive was not immediately known.

According to the university, Tooley began firing the AK-47 near the Littlefield Fountain at about 8:10 a.m. Officers from the University of Texas Police Department and the Austin Police Department pursued Tooley, who went into the Perry-Castaneda Library.

Authorities said earlier they were searching for a possible second suspect, but Robert Dahlstrom, chief of staff in the Austin Police Depart, said they now do not believe there is one.

"A suspected shooter in PCL library is dead," said an alert posted on the university's emergency website at 10:30 a.m. "If you are off campus, STAY AWAY. If you are on campus, lock doors, do not leave your building. All organized classes for today, September 28, are canceled."

The campus had been on lockdown since an alert went out, but spokeswoman Rhonda Weldon said students were allowed to leave, and shuttle buses were to transport students and staff away from the campus. The university canceled all classes for the day.

An ambulance was seen just before 9 a.m. in front of the Perry-Castaneda library, CNN affiliate KXAN reported. SWAT teams, armored vehicles and helicopters surrounded the campus.

"I extend my sympathy to the family, friends, and classmates of the young student who took his life," said university President Bill Powers, who thanked police for their response to the emergency. "In the days ahead we will attempt to understand his actions and to learn from this tragedy."

University of Texas professor Randall Wilhite heard gunshots on his way to class and saw students scrambling to safety. He said he saw a man in a dark suit and a ski mask pulled over his face running toward the direction of the library a little after 8 a.m.

Wilhite said the man was carrying what appeared to be an assault rifle and fired it randomly.

"When I pulled up in my car, he stood right in front of me and didn't stop running but turned in my direction, fired three shots into the ground to the left of my car and kept running. I wasn't sure it was real until I saw the bullets strike the ground to my left."

Student Micah Geisenberg was already on a bus to the university when he received an e-mail alert to stay away.

"It's chaos right now," said Geisenberg, who heard a gunshot as he got off the bus near the library.

Matt Holiner heard a series of loud bangs from his dorm room, a couple of blocks south of the library. He suspected they might be gunshots, especially when he saw people running away. By mid-morning, there were at least 10 police cars outside his window.

"It's been quite an exciting morning to say the least," he said.

The library is about two blocks from clock tower, where student Charles Whitman went on a shooting spree after killing his wife and mother. On August 1, 1966, Whitman, 25, killed three people in the tower and then another 10 from the tower's observation deck before police shot him dead. His actions were blamed on narcotics abuse coupled with health, family and legal problems.